Permanently energized synchronous machines are usually used as the electric drive in modern hybrid vehicles. Permanently energized synchronous machines include a rotor in which the magnets generating the magnetic flux are situated as well as a stator having stator windings. The electric machine generates a torque which depends in particular on the phase current and on the magnetic flux in the machine. The generated torque determines the acceleration and/or response characteristic of the vehicle and thus constitutes an important variable that must be determined.
In traditional vehicles, the torque of the electric machine is usually calculated by a mathematical model. Under the assumption that there is no reluctance torque, the following equation applies for torque M:M=K*Iq*ψ,where:K: machine constantIq: transverse current in the machine (field-oriented regulation)ψ: magnetic flux in the machine.
However, the calculation of torque M is relatively inaccurate because magnetic flux ψ is not constant and in particular varies as a function of temperature. This often results in a relatively high error.